Solar panels, also known as photovoltaic (PV) modules, are increasingly being used for electric power generation, in applications ranging from residential to utility-scale installations. Such installations are known as PV arrays. The accumulation of dust, dirt, and other contaminants, collectively known as soiling, on PV arrays reduces their power output by blocking light transmission to the PV devices. Soiling can be a significant loss factor, especially in dusty regions without frequent rainfall. Soiling losses are variable and depend on weather conditions; therefore they must be determined at each installation site.
Owners and operators of PV arrays often wish to measure their power loss due to soiling. Motivations include pre-construction site surveys to estimate the impact of soiling on the performance of a planned PV array project, validation of as-built PV array performance compared to predictions and contractual performance guarantees, and optimization of PV module wash schedules at operating sites in order to yield greatest return on investment for the expense of washing.
A number of systems have been developed for the measurement of soiling losses on PV arrays. These systems involve, in various forms, comparing the output of two PV reference devices, one of which is kept clean (the “clean PV device”), and the other of which is allowed to accumulate soiling at the same rate as the PV array (the “soiled PV device”). By comparing the electrical output of the soiled PV device to expectations based on the clean PV device, the degree of power loss due to soiling can be estimated.
In existing systems, the clean PV device is maintained clean either manually, by operations and maintenance personnel, or automatically, by equipment using a water spray or other cleaning action.
However, both the manual and automatic cleaning methods have an impact on cost of ownership. Manual cleaning requires a labor expense, which may be significant considering that cleaning should ideally be performed daily in order to obtain the best measurements. Automatic systems minimize the labor expense, but incur a capital expense.
Both automatic and manual cleaning approaches for soiling measurement systems may be practical at large utility-scale installations, where labor and/or capital expenses are typically warranted, but the expense of such systems limits their utilization. Furthermore, the systems are less practical at smaller installations, including large roof-top commercial-scale PV arrays, which cannot afford dedicated labor or equipment capital expense.
Therefore, there is a need for an improved soiling measurement device that is less expensive to deploy and maintain and is suitable for a larger range of installation types.